Trim components such as trim panels are typically used for covering and finishing the interior passenger cabins of automobiles, aircraft, rail vehicles, etc. as well as luggage areas and some external areas of such vehicles. For example, in automotive applications such trim components include headliners, door liners, armrest pads, storage bins, consoles, dashboard covers, load floors, package trays, pillar covers, trunk liners, carpeted floor liners, engine hood covers, wheel well liners, etc.
Such trim components typically are produced as single-layer or multi-layer press-molded and thermoformed components of composite materials, which may include natural and/or synthetic fibers of organic and inorganic basis, as well as a synthetic plastic binder of a thermoplastic or thermosetting character. It is known to fabricate such trim components from a great variety of different materials providing different required functional properties, such as a visually attractive and esthetically pleasing surface covering that is also comfortable to the touch, as well as providing thermal and/or acoustic insulation, absorption and damping. Typically, a trim component such as a trim panel includes a cover layer (also known as a “decor” layer) laminated onto a substrate, whereby the cover layer provides the visible or exposed face side of the trim component, and the substrate forms the mounting surface or back side of the trim component and provides the required structural strength and three-dimensional form of the component. One or more additional layers, such as foam padding and thermal or acoustic insulation layers, may be laminated between the cover layer and the substrate. The substrate may be made of various materials, for example synthetic plastic, fiber board stock including wood fibers or other natural fibers embedded in plastic resin, fiberglass, or a hybrid composite including natural fibers together with synthetic plastic fibers. The plastic materials may include thermoplastic and/or thermoset materials. The cover layer may be made of decorative woven or non-woven fabric, fleece, natural leather, imitation leather, carpet, or vinyl or other plastic sheet materials, preferably bonded to a backing of a foam material.
Various methods are known for press-molding such trim components. For example, a sheet of the substrate material, a sheet of the cover layer material, and one or more sheets of any intermediate layers are stacked to form a sandwich structure, which is then heated, laminated together, compressed, and pre-calibrated to a particular thickness between parallel planar press plates, which may be heated to a suitable temperature so as to heat and thereby melt or soften thermoplastic materials and/or activate and accelerate a chemical thermosetting reaction of thermoset materials of the component layers. With or without such an optional pre-laminating and pressing step, the stack of material layers is placed between a three-dimensionally contoured lower mold and a three-dimensionally contoured upper mold of a molding press. One of the molds is typically a female or cavity mold tool and the other mold is typically a male or core mold tool that mates with the female or cavity mold tool to form a molding cavity gap therebetween, in which the trim component material layers are to be pressed and molded to the three-dimensional contoured shape of the mold tools. The upper and lower molds are closed relative to one another, and thereby the layered sandwich structure is further laminated, compressed and three-dimensionally molded, under the effects of heat and pressure between the contoured upper and lower molds. Generally in this regard, the cover layer and substrate materials are thermoformable, i.e. so that they may be heated to a softening or molding temperature, then molded into a desired three-dimensionally contoured shape, and then cooled to “freeze” included thermoplastic materials, or to chemically set included thermosetting materials, to become rigid and maintain the molded contoured shape.
The mold tools typically further include a pair of cooperating bypass cutting edges, or a pinch edge that cooperates with a counter surface on the other mold tool, by which an edge of the trim component is bypass-cut, or stamp-cut or pinched, respectively when the mold tools close relative to one another. Forming an exact or precise trimmed edge of the trim component, perpendicularly to the local surface of the molding tool, along the perimeter of the trim component is extremely important for the appropriate fit, finish and appearance of the trim component in its final installed application. However, due to tolerances and misalignments that can arise during the laminating and molding process, and due to the stretching and three-dimensional molding deformation of the cover layer and the substrate during the molding process, the various layers of the trim component may stretch, shrink, retract or pull-back by differing extents at the edge of the trim component. Particularly, due to different stretching and retraction characteristics of the materials, in some cases the edge of the visible surface cover layer and/or the edge of the back side substrate layer may pull-back or retract away from the intended edge position during the molding process. Such shrinkage or pull-back can arise perpendicularly or also diagonally or obliquely relative to the cross-section of the component. Such variable shrinkage, retraction or pull-back of the edge of one or more layers of the component is unacceptable and can lead to a finished trim component being rejected due to unacceptable edge quality, therefore leading to increased waste and lower yield of the production process.